The present invention relates to a device for cleaning a circulating screen serving to form a fiber web (e.g., a paper web). The invention takes its departure from the subject of WO 92/13132.
As is known, a paper-making machine has an endlessly circulating screen serving to dewater a fiber suspension in order to form a paper web therefrom. This web is then removed from the screen and fed to subsequent processing stations (a pressing and a drying part, for example). The endless screen then returns to the point where the fiber suspension is added. During this return run, the screen must be cleaned; in particular, adhering fibers and filler particles must be removed.
The cleaning device suitable for this purpose and described in WO' 132 essentially comprises a blowing device extending transversely with respect to the screen travel direction, said device forming a gap relative to the screen travel direction with the screen in front of a blowing opening, said gap tapering in the manner of a wedge. A water spray device terminates in this gap. Thus, a film of water is formed on one side of the screen, onto which the air stream (emerging from the blowing opening) impinges. The air stream thus forces the water through the screen mesh, loosening and carrying away dirt particles from the screen. It is also known that a screen-cleaning device of this kind can be used when the paper web formed on the screen is removed from the screen during normal operation, but in this device, however, the web is released from the screen during the starting phase by means of the cleaning device and must be guided into a waste separator. The use of such a screen-cleaning device in a double screen section is also known, in which the initial web formation takes place between two screens. In this case a screen-cleaning device can be provided in the return run of each of the two screens.